Frequently, two or more belts are used in a belt drive to transmit power from a drive member, such as a drive pulley, to a driven member, or members, such as driven pulleys. In some instances, two or more belts are required primarily because of the large amount of power which must be transmitted. In other instances, two or more belts are used primarily to provide different speed ratios to the different devices being driven. In either event, the two or more belts are used in an independent manner, each mounted separately from the other.
In the copending United States patent application of L. J. Stephanoff, Ser. No. 422,250, filed Dec. 6, 1973, and assigned to the same assignee as the present invention, a belt drive system is disclosed in which power is transmitted from a drive pulley to driven pulleys through the use of two belts, one of which is mounted directly on the other, in "piggyback" fashion, at the drive pulley. The inner belt through its side walls provides a good gripping engagement with the side walls of the drive pulley, while the outer belt has the flexibility and strength to transmit the power between the inner belt and the driven pulleys. Gripping contact between the two belts is provided by mutually engaging teeth on the outer surface of the inner belt and on the inner surface of the outer belt.
In the copending United States patent application of Avramidis and Partridge, Ser. No. 486,261, filed 7/5/74, a piggyback dual belt drive arrangement is used to drive two separate sets of automobile accessories, one set being driven by one of the stacked belts and the other set being driven by the other stacked belt.
It has been known heretofore to provide belts having one surface with alternate ridges and grooves to mate with alternate grooves and ridges on a pulley.